The present invention relates generally to casing valves for use in the casing of a well, and more particularly, but not by way of limitation, to cementing tools constructed for placement in a well casing.
In the drilling of deep wells, it is often desirable to cement the casing in the well bore in separate stages, beginning at the bottom of the well and working upward.
This process is achieved by placing cementing tools, which are primarily valved ports, in the casing or between joints of casing at one or more locations in the well bore, flowing cement through the bottom of the casing, up the annulus to the lowest cementing tool, closing off the bottom, opening the cementing tool, and then flowing cement through the cementing tool up the annulus to the next upper stage and repeating this process until all stages of cementing the well are completed.
Some prior art cementing tools used for multi-stage cementing have two internal sleeves, both of which are shear-pinned initially in an upper position, closing the cementing ports in the tool. To open the cementing ports, a plug is flowed down the casing and seated on the lower sleeve. Fluid pressure is then increased in the casing until sufficient force is developed on the plug and sleeve to shear the shear pins and move the lower sleeve to the position uncovering the cementing ports. Cement is then flowed down the casing and out the ports into the annulus. When the predetermined desired amount of cement has been flowed into the annulus, another plug is placed in the casing behind the cement and flowed down the casing to seat on the upper sleeve. The pressure is increased on the second plug until the shear pins holding it are severed and the upper sleeve is moved down to close the cementing ports. One such cementing tool of this type is disclosed in Baker U.S. Pat. No. 3,768,556, assigned to the assignee of the present invention.
An external sleeve cementing tool which uses a mechanical inner locking means between an inner operating sleeve and an outer closure sleeve is disclosed in Giroux et al. U.S. Pat. No. 5,038,862 (the '862 patent), assigned to the assignee of the present invention. This external sleeve cementing tool is particularly useful in completing stage cementing of slim hole oil and gas wells. Slim hole completions involve using casing inside relatively small hole sizes to reduce the cost of drilling the well. In other words, the well annulus between the borehole and the casing is relatively small.
It is important that the sleeve utilized to close, or block the cementing port remain in the closed position, so that after the cementing operation is complete, any plugs in the casing can be drilled out, and fracturing/stimulating can be performed with no leakage. Current external sleeve cementing tools, like that shown in the '862 patent, include exposed locking grooves that may become partially filled with debris, thus preventing proper engagement of lock rings. If the closing sleeve does not properly lock in the closed position, drill-out and/or pressure created during stimulation treatments can push the sleeve open so the stimulation fluid leaks through the cementing port. The leakage can damage the integrity of the cement, negatively impact the stimulation treatment, and can cause the breakdown of zonal isolation.